"year"	"calls"
1950	4.4
1951	4.7
1952	4.7
1953	5.9
1954	6.6
1955	7.3
1956	8.1
1957	8.8
1958	10.6
1959	12
1960	13.5
1961	14.9
1962	16.1
1963	21.2
1964	119
1965	124
1966	142
1967	159
1968	182
1969	212
1970	43
1971	24
1972	27
1973	29